The present invention relates to a parallel connection of infinitely-adjustable looping gearings, with at least two belt pulleys mounted axially side by side on a driving or driven shaft.
If a number of infinitely-adjustable looping gearings, in particular stepless V-belt gearings, are operating in parallel, in order to increase the transmissible power, then the problem arises of maintaining an equal transmission ratio between all the individual gearings in order to avoid incorrect differences of tension between the different V-belts. This problem of ensuring indentical transmission ratios can be avoided, for example, if the driving pulleys for the V-belts are driven via differential or planetary gearings. It is permissible for the pulleys driven by these latter to rotate at different speeds, so that despite not exactly identical transmission ratios in the sets of pulleys operating in parallel no undesirable tension differences will occur between the different V-belts.
It is true that this use of differential or planetary gearings ensures more or less faultless operation of the V-belt gearings operating in parallel, but since these differential or planetary gearings, in the systems hitherto known, have to run in an oil bath, it necessitates at least one oil-tight housing, so that it is only at considerable cost that it is possible to construct a functional and compact combination of such differential gearings with belt gearings that operate dry. Furthermore, the over-all efficiency of such a combination is reduced by the power losses ocurring in the differential gearings used.
For the avoidance of undesirable tension differences between the different belts of a parallel gearing, the prior art includes a fundamentally different solution in which the differences between the torques which are transmitted by the individual sets of pulleys are utilized by means of suitable mechanisms for correcting the belt running gap width between the sets of pulleys. Constructional solutions according to this principle are based on the utilization for regulating purposes, for example, of the axial thrust occurring in the individual pulleys, on the assumption that this axial thrust is in exact proportion to the torque transmitted. Devices of this kind are already known from U.S. Pat. No. 2,158,047 and German Pat. No. 1,042,332. The sphere of application for these solutions is thus limited to stepless looping gearings, in which the said assumption is in actual fact correct.
The two aforementioned systems devised for the avoidance of incorrect belt tension differences in parallel gearings, i.e., the use of differential gearings in accordance with the prior art and also the utilization of torque differences for regulating purposes, are found to suffer in common from the drawback that in each of these load distribution devices according to the prior art, it is necessary for a control rod system, for example, to act on each of the controlled halves of the pulleys, so that the operation of a large number of sets of pulleys in parallel leads to the creation of a complicated control mechanism, by which the space occupied by a gearing of this kind is increased to an undesirable extent. This also applies, moreover, to a stepless V-belt gearing which has become known in the motor car industry and in which the transmission ratio is controlled by centrifugal weights and vacuum cylinders.